Aqueous humor is naturally produced within the posterior chamber of the eye and serves a beneficial role to the health and function of the eye itself. Most notably, the aqueous humor provides nutrition, such as amino acids and glucose, to various ocular tissues while simultaneously pressurizing the eye and maintaining the correct intraocular structure. For this reason, aqueous humor is continuously produced and drained from a healthy eye to provide these important nutrients and maintain proper intraocular pressure.
Normal intraocular pressure is generally between 10 mmHg and 20 mmHg. In order to maintain this pressure, aqueous humor inflows from the posterior chamber of the eye into the anterior chamber of the eye. Aqueous humor circulates throughout the anterior chamber where it nourishes the cornea, before exiting through the trabecular meshwork and into Schlemm's canal. From there, it flows into the surrounding lymphatic channels. Under normal, healthy conditions, this cycle of inflowing and outflowing aqueous humor continues unabated. However, in some instances, the drainage of the aqueous humor begins to slow due to an obstruction in the outflow from the eye. Because the inflow remains the same while the outflow decreases, intraocular pressure within the eye begins to increase over time. Generally, intraocular pressures over 20 mmHg are considered a higher risk for damaging the optic nerve, and may result in glaucomatous optic nerve loss. The effects of glaucoma are irreversible and, if left untreated, may lead to partial or complete blindness. In the United States alone, more than 120,000 people have been diagnosed as clinically blind as a direct result of the debilitating effects of glaucoma. In fact, about 10% of all blindness in the United States is caused by glaucoma. In the event glaucoma is detected in a patient, it is important to quickly and effectively reduce intraocular pressure within the eye in order to prevent further damage to the optic nerve and preserve the patient's remaining vision.
Various treatments for glaucoma have been developed, but with mixed results. Initially, glaucoma may be treated with medication in the form of eyedrops or pills to either decrease the inflow or increase the outflow of aqueous humor. If this treatment fails, surgery may be necessary to reduce intraocular pressure. This can involve laser procedures which treat the trabecular meshwork resulting in increased outflow, or treat the production site of aqueous humor, the ciliary body, resulting in reduced inflow. Other surgical procedures for treating glaucoma generally involve creating a drainage system within the eye for directing aqueous humor from the anterior chamber to another location within or around the eye to be reabsorbed by the lymphatic system. Frequently, a surgeon directs the aqueous humor to a bleb formed with the conjunctiva tissue under the conjunctiva itself. This fluid connection to the bleb creates a sealed system in which the aqueous humor travels. Unfortunately, the healing characteristics of the eye work against the formation and maintenance of the bleb. As such, blebs are prone to scar down to the conjunctiva and/or become encapsulated, effectively blocking the outflow of the aqueous humor and, once again, increasing intraocular pressure.
In order to reduce the likelihood of bleb failure, plates may be placed on top of the sclera and sewn against the sclera in order to create additional space to maintain the bleb. Generally, the additional space creates a larger bleb, thus reducing the likelihood of the bleb scaring down. While this has proven mildly successful, the system must be sewn absolutely watertight or the bleb will still leak, scar down, and fail. Such watertight seals are often times difficult to form and extremely time consuming to create. Similarly, the fluid connection to the anterior chamber also is at risk for scaring closed or completely plugging with adjacent iris tissue. To some extent, valve implants may also be used to maintain these fluid connections and facilitate the outflow of aqueous humor. Unfortunately, for many patients, these too can become surrounded by tough fibrous inflammatory tissues, called encapsulation, rendering the entire procedure ineffective.
Moreover, these leaks, bleb failures, and fluid connections are difficult to detect in the time immediately following the surgery. For this reason, repeated follow-up visits to the surgeon are required. Should the bleb fail over time, the patient has few, if any options to repair the bleb. Typically, the patient must undergo another time consuming, complex, tedious surgery hoping to create a new bleb prone to the same, inherent risks of failure.
There is a need for a method and device for reducing intraocular pressure, particularly in the treatment of glaucoma, that addresses present challenges and characteristics such as those discussed above.